The present invention relates to a self-extinguishing expansion switch or circuit breaker for high or medium voltages.
It is state-of-the-art, for example according to the document EP-A-0,298,809, to provide a circuit breaker with a sealed enclosure filled with a high dielectric strength gas and containing one or more poles of the circuit breaker, each pole comprising:
an extinguishing chamber having a revolution surface sealed off tightly at opposite ends by end-plates; PA1 a pair of tubular arcing contacts, arranged coaxially in said extinguishing chamber and each passing through one of the end-plates to make the extinguishing chamber communicate, in the separated position of the arcing contacts, with the enclosure forming an expansion chamber by the gas outflow ducts constituted by the tubular arcing contacts; PA1 a coil or permanent magnet supported by one of the end-plates inside the extinguishing chamber so as to create in the separation zone of the arcing contacts a magnetic field for blowout in rotation of an arc drawn between the separated arcing contacts; PA1 a pair of main contacts located outside the extinguishing chamber and arranged to open before separation of the arcing contacts takes place when an opening operation of the circuit breaker is performed. PA1 on the one hand an extinguishing cheer, a first end-plate of which is conducting and forms a first current terminal pad which is connected, in this extinguishing chamber, to a stationary annular arcing contact, and the other end-plate of which is insulating and has passing through it a coaxial and axially movable conducting tube, the free end of this tube supporting the movable annular arcing contact which is the conjugate of the stationary arcing contact: PA1 and on the other hand a sealed expansion chamber, of much larger dimensions, which is tightly connected to this extinguishing chamber by at least one duct designed to enable the ionized gases to migrate, when an arc is created on opening, from this extinguishing chamber to this expansion chamber; PA1 this expansion chamber being coaxial to the extinguishing chamber and containing the main contacts of the pole, comprising a stationary contact which is connected to the conducting end-plate of the extinguishing chamber and a movable contact which is normally designed to be connected to said movable conducting tube, mechanical means being provided to open these main contacts before the arcing contacts, this switch or circuit breaker being characterized in that: PA1 the extinguishing chamber is not placed inside the expansion chamber, but in the extension of and above the latter; and PA1 the movable conducting tube which supports the movable arcing contact electrode at its free end is designed, in the closed position and when it is withdrawn to its open position with the arc finally extinguished, to be in electrical contact with a second coaxial conducting tube, these two tubes being arranged and means being provided to separate the tubes electrically and axially from one another, when the movable tube is further withdrawn beyond this open position with the arc finally extinguished, thus achieving between them a sufficiently large gas gap so that the voltage is in fact applied via the external tubular insulating part which constitutes the expansion chamber enclosure, and not via the insulating annular end-plate of the extinguishing chamber.
A circuit breaker of this kind with self-extinguishing expansion and rotating arc combines pneumatic blowout of the arc by expansion gases with magnetic blowout of the arc in rotation on annular electrodes. This breaking method can be used in medium or high voltage circuit breakers and presents the advantage of requiring low operating energies.
It does however present some drawbacks, especially when operation is desired in the high voltage field.
A first drawback is of purely dimensional nature. If we consider a pole of this state-of-the-art circuit breaker (e.g., see FIG. 1 of the above-mentioned document EP-A-0,298,809) it can be noted that the extinguishing chamber, itself of relatively small dimensions, is surrounded by a rather voluminous insulating enclosure. It is in fact necessary, for this state-of-the-art achievement, to arrange a sufficient expansion volume both above and below the extinguishing chamber, and moreover to provide a fairly wide annular communication corridor between these two, upper and lower, expansion volumes. The dimensions of the tubular insulating part, generally made of porcelain, of the sealed enclosure containing each pole of the circuit breaker are subsequently large which, especially for high voltages, is particularly disadvantageous in terms of space requirements and cost price.
Another drawback lies in the fact that, when the circuit breaker pole is open, all the voltage is applied via the insulating ring which forms one of the two end-plates of the extinguishing chamber, the other end-plate forming part of a conducting bell which is closed by this insulating ring. This does not cause great problems for a medium voltage for example of about 10 kilovolts, but it can easily be understood that it becomes more difficult to achieve with a high voltage of about 200 kilovolts for example.
Finally, the fact that the extinguishing chamber is positioned well inside the insulating enclosure makes it unsuitable for various advantageous possibilities of mechanical fixing.